exprops3.hpp

C++ Templates 完全导引范例

/* The following code example is taken from the book
 * "C++ Templates - The Complete Guide"
 * by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
 *
 * (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
template<typename T, typename A1, typename A2>
class A_Subscript {
  public:
    // constructor initializes references to operands
    A_Subscript (A1 const & a, A2 const & b)
     : a1(a), a2(b) {
    }

    // process subscription when value requested
    T operator[] (size_t idx) const {
        return a1[a2[idx]];
    }
    T& operator[] (size_t idx) {
        return a1[a2[idx]];
    }

    // size is size of inner array
    size_t size() const {
        return a2.size();
    }

  private:
    A1 const & a1;    // reference to first operand
    A2 const & a2;    // reference to second operand
};